1. Field of the Invention
This invention relates generally to a quasi-optical gyrotron for the production of electromagnetic radiation in the form of mm waves and particularly to a quasi-optical gyrotron, in which electrons running on an electron beam axis are forced to gyrate by a static magnetic field aligned parallel to the electron beam axis and excite an electromagnetic alternating field in a high-power resonator.
2. Description of the Background
A quasi-optical gyrotron is known, e.g., from Swiss Patent 664045 or the article "The Gyrotron, Key Component for High-Power Microwave Transmitters," H. G. Mathews, Minh Quang Tran, Brown Boveri Review 6-1987, pp. 303-307. In comparison with the conventional cylindrical gyrotron this gyrotron has the advantage that it can produce a greater power. The reason for this resides, i.a., in the following facts:
1. Since the resonator is not coaxial, but perpendicular to the electron beam axis, it can be dimensioned independently of the "klystron part." Especially the radiation exposure of the resonator mirrors and HF gaps can be reduced by enlarging the diameter.
2. The energy present in the resonator can have two outputs.
Basically it is desirable that the gyrotron have as great an efficiency as possible. Therefore, in the above-cited publications it is proposed to place a control resonator ahead of the power resonator. The control resonator bunches ("prebunching") the electrons so that the electrons arrive with the suitable phase angle in the subsequent power resonator.
But besides the improvement of efficiency, the actual power of the output radiation is of special interest. It has been shown that the development of high-power gyrotrons (P greater than 500 kW continuous wave) reaches its limits due to the load carrying capacity of the gaps, by which the radiation produced in the resonator is output from the evacuated tube. Also with optimal transparency, these gaps would have to be heated in the desired power range so greatly that they would break in a very short time.
It is indeed known that the load limit can be pushed back if the gap is made from two separated disks, between which a liquid circulates and thus provides laminar cooling. But such a measure is not sufficient if it is a question of achieving radiation power in the megawatt (MW) range.
An important aspect with gyrotrons is the large but unavoidable expense of auxiliary units (superconducting coils, vacuum units, power supply). Of course, they should be kept as small as possible and at the same time achieve their function. This, e.g., is the case if a unit be used for different purposes.